US2265473A - Coating composition - Google Patents

Description

Patented Dec. 9, 1941 7 2,265,473 COATING COMPOSITION Joseph W.

ner

Douglas Ca'nnell, to The Sherwin-Williams Company,

Lakewood, Ohio, as-

Clevelan Ohio, a corporation of Ohio No Drawing. Application July 11, 1939,

Serial No. 283,806

. of my invention will be apparent from. the fol- This invention relates to coating compositions and has for its main object the provision of a coating composition or paint having high reflectance power for the light radiations or colors of the visible spectrum and also a relatively high degree of absorption of the infra-red or heat radiations.

A coating composition orpaint embodying my invention is especially adapted for use in improving artificial illumination and may be applied to ceilings and other surfaces where it is desired to have a substantially white reflecting surface for assisting in illuminating some space or object with a high degree. of intensity. Commonly used white pigments such as zinc oxide, white lead and titanium oxide have a high reflectance power of infra-red rays, as well as of the visible colors, with the result that the white coating compositions that have heretofore been available are objectionable when a high intensity of artificial illumination is to be used. The reason for this is that the infra-red or heat radialowing description.

My investigations have been made principally with the common incandescent electric lamps.

tions, which emanate from the source of arti- 'iicial illumination being used, are reflected by such known coating compositions and when these radiations are absorbed by objects or persons in the space being illuminated the radiant energy is converted into sensible heat.. This radiant energy produces a heating effect on the skin and body of persons working in strongly illuminated places such as moving picture studios, drafting rooms and the like, which is very uncomfortable and highly objectionable.

As will be explained more in detail hereinafter my invention overcomes this difflculty by providing a coating composition which is capable of absorbing, to a relatively high degree, the infra-red or heat radiations emanating from a source of artificial illumination. My composition is therefore especially adapted for use in coating the ceiling and walls of rooms requiring a high degree of illumination, and also for .coating reflectors for high intensit lamps.

My invention is also applicable to coatings for articles such asv radio cabinets, vacuum which it may bedesirable -to produce a baked finish by infra-red radiations since the incorinfra-red or heat rays.

Various other objects and possible applications cleaners, bicycles, automobile bodies, etc, on

' was complete reflectance of In such lamps it may be assumed that about 11% of the energy that is put into the lamp is radiated in the form of visible energy; that is to say wave lengths of about 4000 to 8000 angstrom units, and about as infra-red energy or wave lengths above 8000 angstrom units. The other 19% is not radiated but is dissipated by conduction and convection. The net effect of the entire energy output has only a slight effect on the actual temperature of the air in the illuminated space. We are, therefore, only concerned with the radiant energy, that isto say the 11% visible radiation and the 70% infra-red radiation. Disregarding the 19% of conducted and convected heat, the visible and infra-red radiations are here regarded as a unit of or the total radiation, of which "about 14% is visible radia-' tionand about 86% is infra-red radiation.

In any case. where the useful energy given off by an incandescent lamp consists of the visible radiation, an ideal coating for a reflecting surface would be one which would reflect all the light, or visible radiation, and which would absorb all the infra-red radiation. Such an ideal coating would thus reflect 14% oiv the total energy, or 100% of the visible radiation and zero per cent of infra-red radiation. A hypothetical coating which would reflect all of thevisible and all of the infra-red would reflect 100% of the total energy, or 100% of the available visible energy and 100% of .the available infra-red energy. The quotient obtained by dividing the total reflectance of the coated reflecting surface by the amount of the visible reflectance constitutes a measure of how closely the ideal is approached, in the case of any particular. coating. The lower this quotient is, the lower is the reflectance of the infra-red energy in comparison with the visible energy. I

In the first example given above where there the visible radiation and complete absorption of the infra-red radiation we would have a total reflectance of 14% and a visible reflectance of 100% and the one-- tientwould be 0.14. In the second case, with a coating composition which completely reflected all of the ,radiant energy, we would have a total reflectance of 100% and a visiblereflectance of 100% and the quotient would be 1.0.

' Studied under the light from ordinary incandescent lamps it has been found that white Basic copper phosphate 7 to are:

senting the quotient of the total reflectance divided by the visible reflectance, from 0.85 to 0.95.

We may represent the quotient aboverefe rred to by the formula 1 RV in which RT represents total reflectance RV visible reflectance. While the and factor of ordinary white paints now on themarket is, as above stated, from 0.85 to 0.95, the

RV factor of a white paint made in accordance with my invention is from 0.45 to 0.50, thus showing a high degree of absorption of the infrared radiation. reflecting visible radiation is about twice as great as its capacity for reflecting infra-red energy.

Atypical paint embodying my invention may be made in accordance with the following formula: Y Y

Zinc oxide (ZnO); "pounds" 1152 The percentage of basic copper phosphate to total pigment may be varied, the

substantial absorption of infra-red.

Paintsmade up substantially in accordance with the foregoing formula, but with variations in the percentage of basic copper phosphate,- in

the total amount of pigment. were found to pro- Copper pyrophosphate, the chemical formula for which is believed to be:

In other words its capacity for 1 (Cu:(PQ4) a.Cu(OH);2) do- 128 Varnish ..gallons 19% Linseed'nil do 9y, Liquid drier do '1 Mineral spirits do 42 .-'I'hese materials will be mixed in the usual way that is employed in making ordinary commercial paints, and it will be noted that of the pigment contained in the paint 90% is zinc oxide, a white pigment, and 10% is basic copper phosphate,

' which is a pale green pigment. The paint has a color which approaches pure white but has a perceptible greenish shade. This paint has a reflection factor for visible radiation from incandescent lamps of approximately '75 to 80%. and a reflection factor for total radiation of 30 to While the above formula comprises zinc oxide as the white pigment and basic copper phosphate as the secondary pigment, the essential inthe secondary pigment and the infra-red absorp- I tion thereby increased, they are objectionable for ,other reasons and most of them have a relatively high tinting efl'ect, because of their color and, therefore, materially-reduce the reflectance of the visible radiations and it is important that the re. flectance of visible radiations be at a maximum. Such compounds as copper sulfate are objectionable because ofbeing water-soluble and, from the commercial standpoint, the paint pigments must be insoluble in water. The basic copper phosphate. appears to be the optimum material for securing the maximum infra-red absorption with a minimum reduction in the reflectance of visible radiation. It has the advantage of having a pale green color of low tinting strength, is insoluble in water,- and does not introduce objectionable characteristics into the paint in which it is incorporated.

When the basic'copper phosphate is incorarticles or surfaces, thereby serving as a means gredient in reducing the amount of infra-red reflectance is the basic copper phosphate. Any of the following commercially used white pigments may be used with thebasic copper phosphate and v the same type of effect, on infra-red radiation, will result. The other white pigments referred Basic lead carbonate Lithopone Zinc Sulfide Titanium Dioxide Basic lead sulfate Leaded. zinc Antimony oxide Silica Magnesium silicate Aluminum silicate Whiting Chlorinated rubber Casein or other water soluble binders for forcing the baking and shortening the time required. 7

In white coating compositions for ceilings, walls and other reflecting surfaces I have found that while an increase in the amount of basic copper phosphate in the pigment will increase the infrared absorption, it will also, because of its tinting effect, reduce the amount of the reflectance of visible radiations and, therefore, I have found that, for commercial purposes, the amount of reflectance of the visible, radiations should not be substantially below and the reflectance of the infra-red should not be above 35%. An increase in the absorption of infra-red, at the expense of reflectance of the visible radiations. must be compensated for by an increase in the Y amount of electrical energy that is put intothe lamp in order to maintain the desired degree of illumination, and, therefore, it does not appear to be economical to increase the amount of basic copper phosphate to such anextent that the reflectance of the visible radiations will be reduced substantially below 75%".

While I have given a specific formula for a paint embodying my invention it will be understood that this is only for the purpose of illustrating a preferred embodiment of my invention figure of 10% being used in the above formula because it gives a relatively high light reflectance together with a sale and that the invention is not limited to the combination of ingredients set forth in said formula, as other materials may be used. in varying proportions and with diflerent vehicles to produce a similar effect. The essential feature of my invention is the discovery that it is possible, by the incorporation of a relatively small amount of basic copper phosphate in a coating composition to reduce, by as much as one-half, the

amount of inira-red reflection without materially or objectionably reducing the reflection oi the visible radiation.

Having thus described my invention, I claim:

' ini'ra-red radiations and consisting of a liquid vehicle with which there is mixed a composite p18- l. A coating composition of relatively high revehicle with which there is mixed a composite pigment the major portion of which is a substantially white pigment having a relatively high:

degree of reflectance oi. Visibleradiations and the minor portion of which is basic copper phosphate.

3. A substantially white coating composition having a relatively high capacityror absorbin ment 01' which not more than 25% is basic copper phosphate and the balance is a substantially white pigment having a relatively high degree of reflectance of visible radiations.

4. A coating composition having a relatively high capacity for reflecting visible radiations oi the spectrum and consisting of a liquid vehicle and pigment material, the major portion of said pigment material consisting of a pigment having a relatively high capacity for reflecting visible radiations and the minor portion of which consists of basic copper phosphate.

5. A coating composition having a relatively high'capacity ior reflecting visible radiations of the spectrum and consisting of a liquid vehicle and pigment material of which not mor than 25% is basic copper phosphate and the balance is a pigment having a relatively high capacity for reflecting visible radiations.

6. A coating composition having a relatively high capacity for reflecting visible radiations of 'the spectrum and consisting of a liquid vehicle with which there is mixed a plurality of pigments of which the major portion has a relatively high capacity for reflecting visible radiations and the minor portion is a copper pigment of low tinting strength and relatively high capacity for absorbing infra-red. radiations.

J QSEPH W. .DOUGLAS CANNELL.